Conventionally, Patent Literature 1 reports a polymer which has a main skeleton of a (meth)acrylic monomer, and has an alkenyl group at the terminal. The polymer is known to be excellent in endurance. However, the polymer has a high viscosity, and has a problem with debubbling properties after coating and causes a problem such as stringiness during coating, and thus, for practical use, the polymer fails to achieve an improvement in workability, unless the polymer is diluted with a low-molecular compound.
In addition, a technique is known for curing a polymer having a (meth)acryloyl group by heating or active energy line application with the addition of an initiator which generates radical species, as in Patent Literature 2. The polymer can be cured in a short period of time by, in particular, ultraviolet irradiation. However, when a polymer has a reactive group, the crosslink density is generally low. As a result, if the product is cured, the cured product obtained will undergo a decrease in elasticity, and also have problems such as surface stickiness produced.
On the other hand, the addition of a (meth)acrylic monomer increases the number of cross-linking points, thus strengthening the cured product, and decreasing the surface stickiness. However, as in Patent Literature 3, the excessively increased additive amount of the (meth)acrylic monomer makes the cured product adhesive, thereby resulting in a failure to prepare an elastic cured product. In addition, the addition of the (meth)acrylic monomer has a tendency to decrease the heat resistance, etc. of the cured product, and make the cured product brittle. In order to apply the polymer compound to a sealing agent or a potting agent, the choice and additive amount of the (meth)acrylic monomer are important factors.